Time-delay relay and method of assembling same

ABSTRACT

A time-delay relay comprising a housing having a chamber in which are mounted a thermally responsive switch assembly and a heater in heat-transfer relation with the switch assembly for heating the latter to effect actuation of the contacts thereof. A pair of heater terminals are positioned in terminal receiving slots in the housing, the terminals being locked into position in the slots upon insertion therein and having terminal contact portions extending into the chamber for conductive electrical contact with the heater. The thermostatic switch is positively held in its installed position within the chamber by means of a retainer on the exterior of the housing. Also disclosed is a method of assembling a time-delay relay in which the various components are inserted into respective openings and chambers in the housing and in which various components are secured together by means of a retainer on the exterior of the switch housing.

United States Patent Hunter TIME-DELAY RELAY AND METHOD OF ASSEMBLINGSAME [75] Inventor: Eugene A. Hunter, Dallas, Tex.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 30, 1973 [21] Appl. No.: 383,937

[52] US. Cl 337/88, 337/102, 337/112, 337/327, 337/354, 337/377 [51]Int. Cl. H01h 61/00 [58] Field of Search 337/88, 102, 107, 112, 337/113,327, 341, 354, 377; 29/623; 174/52 [56] References Cited UNITED STATESPATENTS 3/1966 Huffman 337/102 X l/1968 Cardin 337/107 X 3,489,976l/1970 Marcoux 337/102 3,518,601 6/1970 Tyler et al. 337/327 3,537,05210/1970 Snider 337/354 Dec. 31, 1974 Primary Examiner-James D. TrammellAssistant Examiner-Fred E. Bell Attorney, Agent, or Firm-John A. Haug;James P. McAndrews; Edward J. Connors [5 7 ABSTRACT A time-delay relaycomprising a housing having a chamber in which are mounted a thermallyresponsive switch assembly and a heater in heat-transfer relation withthe switch assembly for heating the latter to effect actuation of thecontacts thereof. A pair of heater terminals are positioned in terminalreceiving slots in the housing, the terminals being locked into positionin the slots upon insertion therein and having terminal contact portionsextending into the chamber for conductive electrical contact with theheater. The thermostatic switch is positively held in its installedposition within the chamber by means of a retainer on the exterior ofthe housing. Also disclosed is a method of assembling a time-delay relayin which the various components are inserted into respective openingsand chambers in the housing and in which various components are securedtogether by means of a retainer on the exterior of the switch housing.

17 Claims, 11 Drawing Figures Pmtmm m 3,858,139

SHEET 10F 3 FIG.I

Pmmw ml 3,858,139

SHEET 30F 3 FIG.6

FIG. IO

TIME-DELAY RELAY AND METHOD OF ASSEMBLING SAME BACKGROUND OF THEINVENTION This invention relates to thermostatic electrical switches,and is particularly concerned with a timedelay relay (TDR) utilizing athermostatic switch assembly for opening and closing an electricalcircuit.

More particularly, this invention is concerned with a TDR in which athermostatic switch assembly is held in position within a housing bymeans of a retainer, and with a simple and fast method of assembling aTDR in which electrical terminals may be inserted into openings in thehousing whereupon they become locked in position in the housing. Inprior art TDRs, the thermostatic switch assembly is adhesive-bonded intoposition in the housing and the electrical terminals for the thermostatheater are riveted to the housing. The adhesive bonding procedurerequired that the adhesive be cured, and this curing cycle increased theassembly time of the unit. Both the application of the adhesive and theinstallation of the rivets involved separate manufacturing steps whichincreased production time and costs. Known prior art assembly procedureshave re- SUMMARY OF THE INVENTION Among the several objects of thisinvention may be noted the provision of a TDR which may be assembledwithout the use of rivets or adhesives; the provision of such a TDR inwhich all parts may be brought together along one axis or plane (e.g., avertical one) thereby to simplify assembly; the provision of such a TDRin which terminals may readily be installed in the housing without theuse of rivets, and the terminals and the thermostatic switch assemblymay be snapped into the housing; the provision of a TDR in which many ofthe components perform multiple functions; the provision of such a TDRwhich has no dead metal parts for holding the unit together; theprovision of such a TDR which, once assembled, substantially precludestampering; the provision of such a TDR which is of rugged constructionand is reliable in operation; and the provision of a method of assemblyof such TDR's which results in a simpler, faster and more economicalproduction. Other objects and features of this invention will be in partapparent and in part pointed out hereinafter.

Briefly, a time-delay relay of this invention comprises a housing havinga chamber with openings in its sidewalls, and a thermally responsiveswitch assembly having contacts and a thermostatic element. The contactsof this switch assembly are movable into and out of engagement with oneanother in response to actuation of the thermostatic element when thelatter is subjected to predetermined temperature conditions thereby tomake or break a first circuit. The time-delay relay further includes aheater for heating the thermostatic element, the heater being energizedby a second circuit. The switch assembly has at least a portion thereofadapted for reception and mounting within the chamber in an operatingposition in which the switch assembly is in heat-transfer relation withthe heater. A retainer is provided on the outside of the housing havingportions thereof extending through the openings in the sides of thehousing for gripping engagement with the switch assembly so as to holdthe latter in its operating position.

This invention also encompasses a method of assembling a time-delayrelay comprising a housing with a chamber having openings for receptionof terminals, a thermostatic switch assembly, a heater for heating theswitch assembly, a pair of terminal members for supplying electricalpower to the heater and a clip for holding the switch assembly relativeto the housing. The method comprises an initial step of inserting theterminal members into the openings in the housing, the terminals beingadapted to snap into place when inserted in the openings thereby tosecure them in the housing with portions of the terminals extending intosaid chamber. Next the heater and the switch assembly are inserted intothe chamber with the heater in electrical contact with the portions ofthe terminals and in heattransfer relation with the switch assembly.Finally, the clip is snapped into openings in the sides of the housingfor engagement with portions of the switch assembly thereby topositively secure the switch assembly in an assembled position relativeto the housing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective viewof a timedelay relay of this invention illustrating a clip for locking athermostatic switch assembly into a housing and also illustratingterminals inserted into openings in the housing with the terminalslocked in position relative to the housing;

FIG. 2 is a side elevation of a time-delay relay of this invention as itappears assembled;

FIG. 3 is a plan view of the housing with the thermostatic switchassembly removed illustrating a chamber for reception of thethermostatic switch assembly and openings in the housing for receivingthe terminals;

FIG. 4 is a bottom view of the housing with the clip and terminalsremoved;

FIG. 5 is a vertical section taken on line 5-5 of FIG. 3 with the switchassembly installed therein;

FIG. 6 is a vertical section taken on line 6-6 of FIG. 2 illustratinggripping engagement of the clip with the thermostatic switch assembly soas to secure the thermostatic switch assembly in an operating positionin the housing;

FIG. 7 is a perspective view of the clip;

FIG. 8 is an enlarged plan view of one of the terminals;

FIG. 9 is a side elevation of the terminal shown in FIG. 8;

FIG. 10 is a plan view of another of the terminals; and

FIG. 11 is a side elevational view of the terminal shown in FIG. 10.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, atime-delay relay (TDR) of this invention is generally indicated at 1. Asbest shown in FIG. 1, the TDR comprises a housing 3 having a chamber 5therein, a thermostatic switch assembly 7 inserted in the chamber and anadditional optional switch assembly 9 stacked on top of switch assembly7 and'actuable concommitantly therewith.

More particularly, thermostatic switch assembly 7 includes a switch body11 having a cylindric lower portion 13 adapted for reception andmounting in chamber of housing 3. Two switches indicated generally atl5a,l5b, are mounted within switch body 11. A snapacting compositethermostatic bimetallic disk or element 17, such as disclosed in US.Pat. No. 1,448,240, is mounted at the bottom of the lower portion 13 ofswitch body 11. Because of its nondevelopable or dished shape thisbimetallic disk will snap from one curvature position to an opposite onein response to a change of temperature so as to provide mechanical powerto make and break the contacts of switches l5a,15b. Bimetallic element17 is mounted on the bottom of lower portion 130f switch body 11 bymeans of a cup 19 having good electrical and thermal conductivity, thiscup, for example, being made of copper. The periphery of disk 17 issupported on an internal shoulder 21 within the cup. At temperaturesbelow the selected snap-over temperature condition, the disk isdish-shaped with its convex side facing up. Upon being heated to apredetermined elevated temperature, the disk snaps over center so thatits top face is concave. Upon cooling belowa second predeterminedtemperature, the disk will return to its original curvature.

As previously mentioned, a second switch assembly 9 may be stacked ontothe top of the thermostatic switch assembly 7, the second assemblyhaving two pairs of switches 27a,27b actuable in response to movement ofthe bimetallic disk 17 as the latter snaps over center. This secondswitch assembly includes an auxiliary switch body 29 within whichswitches 27a,27b are mounted and a cover 31 for enclosing them. Switchesl5a,l5b and 27a,27b may control separate independent or relatedelectrical circuits. These switches are essentially identical and eachincludes quick-connect terminals 33a,33b secured, as by riveting, toeither switch body 11 or 29. A flexible contact arm 35 carrying acontact 37 on its free end is secured to each terminal 33a and a contact39 is mounted on each terminal 33b within switch body 11 and 29. Eachmovable arm 35 biases its contact 37 into engagement with a respectivemating contact 39 to maintain the contacts normally closed during theheated mode. For ceratin applications, double-throw switch arrangementsutilizing switch contacts 41 may be provided in cover 31, thesedouble-throw contacts being engageable by back contacts 43 carried byswitch arms 35 of switches 27a,27b. Terminals 44 are provided forconnection of a separate or related electrical circuits to double-throwcontacts 41. it will be understood that any one or more of theseswitches may be inverted and their switch arms biased away from acontact-closed mode whereby they are normally open switches, and thatthe arrangement of disk and switches may be such that contact arms maybe lifted or permitted to move downwardly on a rise of temperature.

As generally indicated at 45, means are provided for actuating flexiblecontact arms 35 in response to bimetallic disk 17 snapping over center.This means is shown to comprise a yoke or bridge 47 bearing against theupper face of disk 17 and having outwardly extending arms 49a,49b. Bores5la.5lb and bores 53a,53b are provided in switch bodies 11 and 29,respectively, and

holes 55a,55b are provided in the flexible arms 35 of switches 15a,l5b.Tubes 57a and 57b are slidably received in respective bores 51a,51b thebottom end of each of these tubes bearing on a respective arm 49a,49b ofbridge 47 and the upper end of the tube being spaced slightly from theundersurface of its respective flexible arm 35 of switches 15a,l5b. Rods59a,59b are received in respective bores 53a,53b in switch body 29, andthese rods extend through holes 55a,55b in flexible arms 35 of contacts15a,15b and into tubes 57a,57b. Rods 59a,59b extend through tubes57a,57b and bear on a respective arm 49a,49b of bridge 47. With disk 17in its heated (concave upwardly) position, the ends of rods 59a,59b arespaced slightly below the undersurface of flexible contact arms 35 ofswitches 27a,27b a distance similar to the distance the upper end oftubes 57a,57b are spaced from their respective flexible contact arms.With the upper ends of tubes 57a,57b and rods 59a,59b spaced from theirrespective flexible arms, as above described, they remain clear of theflexible arms during any creep of the bimetallic disk before it snapsover center from its concave position.

A heater 61 for heating bimetallic element 17 to a predeterminedelevated temperature is mounted in heat-transfer relation with switchassembly 7, this heater being adhesive-bonded to the bottom face of cup19. This heater is pill-shaped and has a characteristicresistivity-temperature curve having a steep-slope positive temperaturecoefficient (PTC) and is more particularly described in coassigned US.Pat. No. 3,489,976.

As shown in FIG. 7, clip 65 is a generally U-shaped member having a baseportion 67 and upstanding legs 69 at the ends of the base portion. Aninwardly extending ear 71 is provided at the top of each leg 69 andcentral lateral extensions 73 project outwardly from each side of baseportion 67 for purposes as will appear. Openings 75 (FIG. 3) areprovided in opposite sidewalls of housing 3, these openings extendinginto chamber 5. The cylindric lower portion 13 of switch housing 11 hasa pair of vertical grooves 77 therein on opposite sides of the cylindricportion. Each groove 77 is closed at its lower end and provides agripping surface or shoulder 79. Clip 65 is made of flexible resilientmaterial (which is also preferably electrically insulative), such asanatural polysulphone. As shown in FIG. 4, housing 3 has a cruciformrecess constituted by crossing grooves 81 in its bottom face forreception of base portion 67 and extensions 73 of clip 65, and also hasvertically disposed recesses 83 in its opposite sidewalls extending downfrom opening 75 for reception of legs 69 of the clip. With the clipinserted in recesses 81 and 83 and with cars 71 extending into openings75, and into grooves 77 in switch body 11, the ears grippingly engageshoulders 79 thereby to hold the switch body in its operating positionand to prevent removal of the switch body from the housing. The clip,when properly seated in housing 3, is flush with respect to the exteriorof the housing. As indicated at 85, a flexible finger is provided at theupper end of each leg 69 for engagement with a portion of housing 3adjacent openings 75, this portion being indicated at 87, so as topositively lock the clip in its installed position in the housing and toprevent disassembly of the TDR assembly. With clip 65 made of flexibleresilient material, fingers 85 are forcibly bent in as ears 71 arepushed into openings 75.

As the ears assume their locking position in engagement with shoulder 79of switch body 11, fingers 85 spring back and engage housing portions87. As shown in FIG. 1, legs 69 may be sprung outwardly to permitinstallation of the clip in the housing 3. Alignment ribs 88 areprovided on the sidewalls of chamber 5 for cooperation with alignmentgrooves (not shown) in the sides of lower portion 13 of switch body 11to insure correct rotational positioning of switch assembly 7 relativeto housing 3.

In accordance with this invention, terminals 630,63b are adapted to besnapped into position in housing 3. As indicated generally at 89,terminal openings are provided in housing 3. As best shown in FlGS. l, 3and 5, terminal openings 89 are parallel to the centerline of chamber 5and are open at the top of the housing. Each terminal has a shank ormounting portion 91 and a contact portion 93a,93b. The mounting portionof each terminal 63a, 63b is essentially the same so that only onemounting portion need be discussed in detail. As shown in FIGS. 9 and11, the shank portion has a quick-connect terminal 95 disposed to extendhorizontally outwardly of hosuing 3 when the terminal is installedtherein, and thus at right angles to shank portion 91. Tabs or barbs 99are struck from the shank at the upper end thereof to project angularlytherefrom, and the contact portion 93 extends from the lower end of theshank. As shown in FIG. 5, the contact portion 93a of terminal portion63a is adapted to reach into chamber 5 and to be in direct electricalcontact with the undersurface of heater 61. The contact portion 93b ofterminal 63b is configured to be in indirect electrical contact withheater pill 61 by contacting cup 19 adjacent the chamber wall, therebyto provide an electrical circuit for energizing the heater. Thus, theterminal portions 93a, 93b, whether directly or indirectly contactingheater 61, are in conductive electrical contact therewith. Terminals63a, 63b are made of resilient metallic material so as to resilientlyengage the heater and the cup thereby to maintain good electricalcontact therewith.

Terminal openings 89 for each terminal 6311,6312 are identical and eachhas a shank-receiving slot 101 and a contact portion slot 103. Terminalopenings 89 are open at the bottom of housing 3 (see FIG. 4) but arecovered by extensions 73 of clip 65 when the clip is in place, therebyblocking access to the lower portions of terminals 630 and 63b. Thecontact slot portions 103 of terminal openings 89 open into chamber 5thereby to permit the contact portions of 93a,93b of terminals 63a,63bto extend into the chamber for conductive electrical contact with heater61. In HO. 5, it can be seen that the upper ends of terminal openings 89open into chamber 5 and with an internal shoulder 105 provided in theshank receiving slots at the upper ends thereof. Upon installation ofthe terminals 63a,63b into respective terminal openings 89, shankportions 91 are received in the shank-receiving slots 101 and the lowercontact portions 93a,93b of the terminal are received in correspondingcontact-receiving slots 103 of the terminal openings 89 with thecontact-receiving slots opening into chamber 5. Upon further insertioninto the openings 89, tabs 99 are forced substantially back intoalignment with shank portions 97 and upon full insertion of theterminals into the terminal openings, the tabs spring out and engageshoulder 105 (see FIG. 5)

thereby firmly to secure the terminals in installed positions withinhousing 3.

In further accordance with this invention, a method of assembling atime-delay relay, includes first inserting terminals 63a,63b intoterminal openings 89 in housing 3 as above described thereby securelylocking them in position as barbs 99 spring outwardly and engage theundersurfaces of shoulders 105. The thermostatic switch assembly 7 isthen installed by inserting the lower portion 13 of switch body 11 intochamber 5 so that heater 61 is in electrical contact with the contactportion 93a of terminal 630 and cup 19 is in electrical contact withcontact portion 93b of terminal 63/). Clip 65 is then moved intoposition to have its base portion 67 seat in cruciform recess 81 as itslegs 69 slide into side recesses 83 of housing 3. Ears 71 of the clipthen snap into openings 75 in the housing so as to engage respectiveshoulders 79 on switch body 11 thereby to hold the switch body inposition relative to the housing. Upon ears 71 being inserted intoopenings 75 in housing 3 and into grooves 77 in switch body 11, fingersspring out and engage the portions 87 of housing 3 thereby to lock theclip thereto and prevent removal of the clip from the housing.

With clip 65 properly seated in recesses 81 and 83 in housing 3, theclip is substantially flush with the exterior of the housing. It will beunderstood that various configurations of clip 65 could be used,including a clip extending around the sides of the housing rather thanacross the bottom. When a clip is used, such as that herein shown whichextends across the bottom of the housing, all parts of the timedelayrelay assembly may be brought into position for assembly along a singleaxis or in a single vertical plane thus enabling simpler and fasterassembly procedures. Also, with the top of housing 3 clear of the clip,add-on switches such as indicated at 25, may be stacked on top of switchassembly 7 without interference from the clip.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. A time-delay relay comprising:

a housing having a chamber therein and openings in its sidewalls;

a thermally responsive switch assembly having contacts and athermostatic element, said contacts being movable into and out ofengagement with one another in response to actuation of the thermostaticelement when the latter is subjected to predetermined temperatureconditions thereby to make and break a first circuit;

a heater for heating said thermostatic element, said heater beingenergized by a second circuit, said switch assembly having at least aportion thereof adapted for reception and mounting within said chamberin an operating position in which said switch assembly is inheat-transfer relation with said heater; and

a retainer on the outside of said housing having portions thereofextending through said openings in the sides of the housing for grippingengagement with said switch assembly so as to hold the latter in itssaid operating position.

2. A time-delay relay as set forth in claim 1 wherein said retainer haslocking portions engageable with said housing thereby to prevent removalof the retainer from the housing.

3. A time-delay relay as set forth in claim 2 wherein said housing has ablind hole in one face thereof constituting the top of the housing withsaid hole constituting said chamber, and wherein said retainer is a cliphaving a portion thereof extending from one side of the housing to theother at the bottom of the housing.

4. A time-delay relay as set forth in claim 3 wherein said openings insaid housing sidewalls are adapted to receive the gripping portions ofsaid clip, each said gripping portion extending into said chamber viaits respective said opening for engagement with said switch assembly.

5. A time-delay relay as set forth in claim 4 wherein said clip is agenerally U-shaped member having a base portion adapted to span thebottom of the housing and upstanding legs extending along opposite sidesof the housing, said legs each carrying said gripping portion and saidlocking portion on the upper end thereof.

6. A time-delay relay as set forth in claim 5 wherein said housing has asecond face constituting the bottom of the housing, a recess in thebottom of the housing for reception of said base portion of the clip andrecesses in said sidewalls for reception of the leg'portions of theclip, said clip being generally flush with the exterior of the housing.

7. A time-delay relay as set forth in claim 5 wherein said housing hasopenings in its bottom, and said base portion of said clip has portionsextending therefrom for covering said openings in the bottom of thehousing.

8. A time-delay relay as set forth in claim 5 wherein said switchassembly portion adapted for reception in said chamber has an upwardlyfacing surface, said gripping portions of said clip extending inwardlyinto the chamber for engagement with a respective said upwardly facingsurface thereby to prevent removal of the switchassembly from thehousing.

9. A time-delay relay as set forth in claim 8 wherein portions of saidhousing are engageable with said switch assembly when the latter is inits assembled operating position thereby forming a seat for the switchassembly in said housing.

10. A time-delay relay as set forth in claim 8 wherein said lockingportion of said clip comprises a flexible fmger engageable with saidhousing when said gripping portion is in engagement with said surfacethereby to prevent removal of the clip from its installed position.

11. A time-delay relay as set forth in claim 1 further comprising a pairof terminals adapted for conductive electrical contact with said heater,said terminals constituting a portion of said second circuit, saidhousing having terminal openings therein for reception of saidterminals, each terminal having means engageable with said housing uponinstallation of the terminal in its respective terminal opening therebyto secure it in the housing.

12. A time-delay relay as set forth in claim 11 wherein each of saidterminal openings extends from one face of said housing constituting itstop face into the housing generally parallel to said chamber, eachterminal opening being at least partially open to said chamber, eachterminal member being insertable into its respective terminal openingthereby to assume an installed position within said housing in which aportion thereof constituting a contact portion extends into said chamberfor conductive electrical contact with the heater, said terminalengagement means comprising a barb angularly projecting from saidterminal, said housing having a portion adjacent each of said terminalopenings adapted for engagement by said barb thereby to secure each ofthe terminal members in its installed position within the housing.

13. A time-delay relay as set forth in claim 12 wherein said housing hasa blind hole in said top face, said blind hole constituting saidchamber, each said opening comprising a slot extending from the top faceinto the housing generally parallel to the longitudinal axis of thechamber and having a first portion spaced outwardly of the chamber and asecond portion opening from the first portion into the chamber.

14. A time-delay relay as set forth in claim 13 wherein said terminalmember comprises a terminal portion adapted to extend from said housingwhen said terminal member is in its installed position, a shank portionadapted to be received by said first portion of said slot and a contactportion adapted to extend from said shank portion into said secondportion of the slot and into the chamber for conductive electricalcontact with the heater, said shank portion having said barb extendingtherefrom for engagement with said housing thereby to prevent removal ofthe terminal from said slot.

15. A time-delay relay as set forth in claim 14 wherein said terminalmembers are made of a resilient, electrically conductive material, andthe contact portion of each terminal is adapted for resilientelectrically conductive engagement with said heater so as to constituteportions of said second circuit.

16. A method of assembling a time-delay relay, said relay comprising ahousing with a chamber and with openings for reception of terminals, 3thermostatic switch assembly, a heater for heating said switch assembly,a pair of terminal members for supplying electrical power to the heaterand a clip for holding the switch assembly relative to the housing, saidmethod comprising the steps of:

inserting said terminal members into said openings in the housing, saidterminals being adapted when inserted in said openings to be secured tosaid housing, portions of said terminals extending into said chamber;

inserting the heater and the switch assembly into said chamber with theheater in conductive electrical contact with said portions of theterminals and in heat-transfer relation with the switch assembly; and

snapping said clip into openings in the sides of said housing forengagement with portions of said switch assembly thereby to positivelysecure the switch assembly in an assembled position relative to thehousing. 17. A method as set forth in claim 16 in which the step ofsnapping said clip into said openings also locks the clip to thehousing.

1. A time-delay relay comprising: a housing having a chamber therein andopenings in its sidewalls; a thermally responsive switch assembly havingcontacts and a thermostatic element, said contacts being movable intoand out of engagement with one another in response to actuation of thethermostatic element when the latter is subjected to predeterminedtemperature conditions thereby to make and break a first circuit; aheater for heating said thermostatic element, said heater beingenergized by a second circuit, said switch assembly having at least aportion thereof adapted for reception and mounting within said chamberin an operating position in which said switch assembly is inheat-transfer relation with said heater; and a retainer on the outsideof said housing having portions thereof extending through said openingsin the sides of the housing for gripping engagement with said switchassembly so as to hold the latter in its said operating position.
 2. Atime-delay relay as set forth in claim 1 wherein said retainer haslocking portions engageable with said housing thereby to prevent removalof the retainer from the housing.
 3. A time-delay relay as set forth inclaim 2 wherein said housing has a blind hole in one face thereofconstituting the top of the housing with said hole constituting saidchamber, and wherein said retainer is a clip having a portion thereofextending from one side of the housing to the other at the bottom of thehousing.
 4. A time-delay relay as set forth in claim 3 wherein saidopenings in said housing sidewalls are adapted to receive the grippingportions of said clip, each said gripping portion extending into saidchamber via its respective said opening for engagement with said switchassembly.
 5. A time-delay relay as set forth in claim 4 wherein saidclip is a generally U-shaped member having a base portion adapted tospan the bottom of the housing and upstanding legs extending alongopposite sides of the housing, said legs each carrying said grippingportion and said locking portion on the upper end thereof.
 6. Atime-delay relay as set forth in claim 5 wherein said housing has asecond face constituting the bottom of the housing, a recess in thebottom of the housing for reception of said base portion of the clip andrecesses in said sidewalls for reception of the leg portions of theclip, said clip being generally flush with the exterior of the houSing.7. A time-delay relay as set forth in claim 5 wherein said housing hasopenings in its bottom, and said base portion of said clip has portionsextending therefrom for covering said openings in the bottom of thehousing.
 8. A time-delay relay as set forth in claim 5 wherein saidswitch assembly portion adapted for reception in said chamber has anupwardly facing surface, said gripping portions of said clip extendinginwardly into the chamber for engagement with a respective said upwardlyfacing surface thereby to prevent removal of the switch assembly fromthe housing.
 9. A time-delay relay as set forth in claim 8 whereinportions of said housing are engageable with said switch assembly whenthe latter is in its assembled operating position thereby forming a seatfor the switch assembly in said housing.
 10. A time-delay relay as setforth in claim 8 wherein said locking portion of said clip comprises aflexible finger engageable with said housing when said gripping portionis in engagement with said surface thereby to prevent removal of theclip from its installed position.
 11. A time-delay relay as set forth inclaim 1 further comprising a pair of terminals adapted for conductiveelectrical contact with said heater, said terminals constituting aportion of said second circuit, said housing having terminal openingstherein for reception of said terminals, each terminal having meansengageable with said housing upon installation of the terminal in itsrespective terminal opening thereby to secure it in the housing.
 12. Atime-delay relay as set forth in claim 11 wherein each of said terminalopenings extends from one face of said housing constituting its top faceinto the housing generally parallel to said chamber, each terminalopening being at least partially open to said chamber, each terminalmember being insertable into its respective terminal opening thereby toassume an installed position within said housing in which a portionthereof constituting a contact portion extends into said chamber forconductive electrical contact with the heater, said terminal engagementmeans comprising a barb angularly projecting from said terminal, saidhousing having a portion adjacent each of said terminal openings adaptedfor engagement by said barb thereby to secure each of the terminalmembers in its installed position within the housing.
 13. A time-delayrelay as set forth in claim 12 wherein said housing has a blind hole insaid top face, said blind hole constituting said chamber, each saidopening comprising a slot extending from the top face into the housinggenerally parallel to the longitudinal axis of the chamber and having afirst portion spaced outwardly of the chamber and a second portionopening from the first portion into the chamber.
 14. A time-delay relayas set forth in claim 13 wherein said terminal member comprises aterminal portion adapted to extend from said housing when said terminalmember is in its installed position, a shank portion adapted to bereceived by said first portion of said slot and a contact portionadapted to extend from said shank portion into said second portion ofthe slot and into the chamber for conductive electrical contact with theheater, said shank portion having said barb extending therefrom forengagement with said housing thereby to prevent removal of the terminalfrom said slot.
 15. A time-delay relay as set forth in claim 14 whereinsaid terminal members are made of a resilient, electrically conductivematerial, and the contact portion of each terminal is adapted forresilient electrically conductive engagement with said heater so as toconstitute portions of said second circuit.
 16. A method of assembling atime-delay relay, said relay comprising a housing with a chamber andwith openings for reception of terminals, a thermostatic switchassembly, a heater for heating said switch assembly, a pair of terminalmembers for supplying electrical power to the heater and a clip forholding the switch asseMbly relative to the housing, said methodcomprising the steps of: inserting said terminal members into saidopenings in the housing, said terminals being adapted when inserted insaid openings to be secured to said housing, portions of said terminalsextending into said chamber; inserting the heater and the switchassembly into said chamber with the heater in conductive electricalcontact with said portions of the terminals and in heat-transferrelation with the switch assembly; and snapping said clip into openingsin the sides of said housing for engagement with portions of said switchassembly thereby to positively secure the switch assembly in anassembled position relative to the housing.
 17. A method as set forth inclaim 16 in which the step of snapping said clip into said openings alsolocks the clip to the housing.